Various alternative patterns of allosteric regulation are utilized in various microbial systems, among them 3-deoxy-D-arabino-heptulosonate 7-phosphate (DAHP synthetase). These regulatory patterns are known to be strongly conserved among the member species of a given genus. It is suspected that interlocking relationships of allosteric control (metabolic interlock) may account for the selective pressure that favors the observed conservatism. The regulatory relationships of other allosteric enzymes with DAHP synthetase is important with respect to the integrated control of the entire biochemical systems. Past and ongoing results obtained at the enzymological and physiological levels will be followed up with detailed analyses at the physico-chemical level. Biochemical and biophysical procedures of protein chemistry will be used to compare each of the DAHP synthetases selected for study. Molecular characteristics of purified proteins will be related to the participation of these proteins in the various distinctive patterns of allosteric regulation which exist.